U.N. Secretary-General Ban Ki-moon on Monday urged Arab leaders to join together in backing Palestinian President Mahmoud Abbas in his efforts to reunite the war-ravaged Gaza Strip with the West Bank.

Speaking a day after Israel and the militant Palestinian group Hamas announced separate ceasefires, Ban also said that Arab unity was crucial if the three-week Gaza conflict was not to be repeated in the future.

"The Palestinians themselves must face the challenge of reconciliation, and work to achieve a unified government under the leadership of President Abbas," Ban told an Arab League summit expected to approve $2 billion in aid to rebuild Gaza.

"I call on all Arab leaders to unite and support this endeavour. We cannot rebuild Gaza without Palestinian unity."